Pitcher Dan Serafini has been handed a 50-game suspension by Major League Baseball after testing positive for a performance-enhancing substance.

The 33-year-old is currently a free agent, having had a brief spell with the Colorado Rockies in 2007.

However, the left-hander has blamed the positive test on substances prescribed to him while he was playing in Japan.

"I did not know at the time that these would cause me to test positive once I returned to the US," he said.

"While playing baseball in Japan, I suffered two significant injuries, and while trying to accelerate the healing process of these injuries, I took substances that were prescribed for me by a doctor in Japan.

"I have not taken these or any banned substances since returning to the US and signing with the Colorado Rockies organization in July."

Serafini has made 102 career major league appearances, playing for the Minnesota Twins, Chicago Cubs, Pittsburgh Pirates, San Diego Padres, Cincinnati Reds and Colorado Rockies.

He pitched for the Chiba Lotte Marines and the Orix Buffaloes in Japan.